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Potential study species

The reproductive biology of Cactaceae is not well known – only approximately 2% of the 2000 or so species have been studied (Mandujano et al, 2010). Consequently, how they interact with neighbouring plants of different species for pollinators or what this means in a community context are both virtually unknown. In one of the few published experiments that explicitly tested these interactions, researchers focused on the highly invasive prickly-pear Opuntia stricta in coastal shrublands in Catalonia (Bartomeus 2008). Cacti in the Opuntia genus are primarily bee-pollinated; they have large, colourful bowl-shaped flowers and many species are rich in pollen and nectar (Mandujano et al, 2010), suggesting they are very attractive to pollinators. Plants that exhibit these characteristics can interact with other plants in two notable ways for pollinators – they may act as a magnet plant, increasing local abundances of shared pollinators and thus facilitating the pollination of their neighbours, or conversely, they may steal pollinators and reduce the fitness of their neighbours.

To determine the effects of the invasion on the native plant community, the researchers created plant-pollinator interaction networks for both invaded and uninvaded sites. They found that O. stricta acted as a super-generalist in its new range. It was visited by 31% of the insect taxa in the invaded sites and was outcompeting native plants for pollination services. Within the same study, they found that Carpobrotus, an invasive succulent, had the opposite interaction with the surrounding plant community; it facilitated the pollination of the native plants in the system. This highlights the species-specific and context-dependent aspects of these interactions. There are a few species of Opuntia common in the Mojave Desert, and I hope to discover if and how they are interacting with other plants, particularly shrubs and their annual understory.